The five pool chemicals every UK owner actually needs, plus a simple weekly routine to keep the water clean, clear and safe all season.
Setting up a swimming pool for the first time, or taking one over from the previous owners, the chemical aisle can feel overwhelming. The good news is that you only need five things to keep a pool clean, clear and safe. Everything else is a nice to have. Here is the essential shopping list, in the order they matter.
This is the non-negotiable one. Sanitiser kills bacteria, viruses and algae. For a UK outdoor pool, chlorine is the standard choice: use granules to top up quickly and stabilised tablets in a dispenser to hold a steady level. Aim for 1 to 3 ppm free chlorine. Bromine is an alternative that suits indoor pools and warmer water.
Chlorine only works properly when pH sits between 7.2 and 7.6. Keep both a pH minus (to lower) and a pH plus (to raise) to hand. In much of the UK we have hard, alkaline tap water, so most owners reach for pH minus far more often. Correct pH also stops the water stinging eyes and going cloudy.
Alkalinity is the buffer that keeps pH stable. Without it, your pH swings wildly every time you add anything. Hold total alkalinity at 80 to 120 ppm using an alkalinity increaser, and your pH becomes far easier to manage. Our guide to alkalinity explains why balancing this first saves you chemicals later.
For any outdoor pool, stabiliser is essential. It acts like a sunscreen for your chlorine, stopping the summer sun from burning it off within hours. Aim for 30 to 50 ppm. Many stabilised chlorine tablets add a little cyanuric acid as they dissolve, so test occasionally to make sure the level does not creep too high. See what pool stabiliser does.
The fifth slot is a two-part rescue kit. Shock is a strong dose of oxidiser that clears out the tired, combined chlorine that builds up after heavy use, restoring that fresh, sparkling feel. A clarifier gathers tiny particles together so the filter can catch them, clearing cloudy water fast. Keep both in the cupboard for when the pool has a busy weekend.
With those five in the cupboard, the routine is easy. Test twice a week. Balance alkalinity, then pH, then top up sanitiser. Shock after heavy use or a spell of hot weather. Run the filter enough hours each day to turn the whole pool over at least once. Do that, and the water largely looks after itself.
Walk down the chemical aisle and you will see plenty of extras: algaecides, metal sequestrants, foam removers, waterline cleaners and more. None of them belongs on the essential list. An algaecide is a useful backup if your pool is prone to algae, and a sequestrant helps if you fill from a well or have staining, but a well-sanitised, balanced pool rarely needs either. Buy them only when a specific problem calls for it, rather than stocking the cupboard on day one. Spending on the five essentials first is what actually keeps the water right, and it keeps your running costs down too.
Sanitiser and pH adjusters are absolutely essential. Alkalinity increaser and stabiliser make the first two work reliably and cheaply, so we count them as essential too. Shock and clarifier are the ones you reach for occasionally rather than every week.
Balance total alkalinity first, then adjust pH, then set your sanitiser and stabiliser. Adding them in that order stops one adjustment undoing another. Always add chemicals to water, never water to chemicals, and let the pump circulate between additions.
The chemistry is the same, but the concentrations and dose sizes differ, so always follow pool dosing for a pool. Compare the trade-offs in our guide on chlorine versus bromine.